1. Field of the Invention
The present invention relates to an adhesive film for a reflection sheet and the reflection sheet using the same. More specifically, the present invention relates to an adhesive film for a reflection sheet and the reflection sheet using the same, in which the adhesive film is manufactured using a plastic base film where heat shrinkage is controlled and thus has superior dimensional stability at a high temperature and excellent workability in a post process for laminating reflection layer, and thus partial detachment of adhesive layer does not occur when the adhesive layer is detached from the adherent, and stable physical properties can be achieved.
2. Background of the Related Art
Owing to the convenience for use, the acrylic adhesives are widely used in industrial fields including advertisement adhesive sheets, reflection sheets, industrial protection films, optical adhesive sheets, adhesive tapes for electronic parts, and the like. And their utilization is spread to as far as display optical films and semiconductor sectors as IT industry is growing-up recently.
Generally, an adhesive film is manufactured by forming an adhesive layer on a release film or a release sheet by coating an adhesive thereon, drying and laminating the adhesive layer on a base film such as a polyethylene terephthalate film. In some cases, the base film may be a pre-processed one depending on its usage.
Possible pre-processing are printing on the base film, or stacking two or more base film, and so on.
Particularly, optical films of various usages are used in flat panel displays (FPD) recently, and such a film has a simply stacked structure or a structure bonded using an adhesive, which includes a panel and a light source. Among the flat panel displays, liquid crystal displays (LCD) have advantages such as thinness, lightness, and low power consumption, and thus they are widely used in various fields including PCs, cellular phones, navigators, TVs, monitors, and the like.
The LCD generally includes a liquid crystal panel, a backlight unit (BLU), and a driving circuit unit for driving the liquid crystal panel. A light source used in the backlight unit may be a Cold Cathode Fluorescence Lamp (CCFL), an External Electrode Fluorescent Lamp (EEFL), a Light Emitting Diode (LED), a Flat Fluorescence Lamp (FFL), and the like, and the backlight unit is divided into an edge type and a direct type depending on the position of the light source. An edge type backlight unit has a light source installed at one end of the LCD and radiates light beams entering from the light source on the liquid crystal panel through a light guide plate and a plurality of optical sheets, whereas a direct type backlight unit arranges a plurality of light sources just below the LCD and radiates light beams entering from the light sources on the liquid crystal panel through a diffusion plate and a plurality of optical sheets.
In order to develop a backlight unit of high luminance, basically, the number of lamps or the driving power of a lamp increases. If the number of lamps or driving power of a lamp increases, temperature of the backlight unit also increases, and thus temperature of the LCD itself increases as a result, which causes malfunctions and failures of various circuit elements. In addition, since large surface LCDs and high performance displays are required, reflection films of high reflectance are demanded in order to improve performance of the backlight unit by supplying light beams to the liquid crystal as much as possible.
As an example of the reflection film, patent document 1 discloses a technique for obtaining a reflection plate having an excellent optical reflectance, which is made of polyester resin containing 2 to 25% by weight of polyolefin, and made by supplying the resin composition into an extruder, pressing the composition into the shape of a sheet, stretching the obtained sheet biaxially to form fine micro voids in the film. However, since the reflection plate is stretched as described above, its thermo-formability is degraded.
In addition, as an example of another conventional technique, patent document 2 discloses a reflection film manufactured by forming a pretreatment film on a surface of PET film, forming a micro-undulated surface by performing corona-discharge on the surface of the pretreatment film, forming a silver film on the micro-undulated surface using a liquid phase injection type deposition method, forming a discoloration preventing film on the silver film to protect the silver film, and forming a protection film on the discoloration preventing film. However, the reflection film may be deformed due to high temperature of the backlight, and thus the reflection characteristic can be degraded. If an adhesive process is performed on a silver reflection film in order to improve the reflection characteristic, the surface of the reflection film may be weak to scratch, and a curing process is required for a certain period of time at room or a high temperature before the reflection film is laminated on the adherent.
Therefore, inventors of the present invention have made an effort to solve the problems of the conventional technique and come to a conclusion that if an adhesive film is manufactured using a plastic base film where heat shrinkage is minimized, it is possible to obtain a reflection sheet without curing after post process for laminating reflection layer such as wet coating, deposition, printing or the like on the back side of the base film. And inventors also found that in case of using the minimized heat-shrinkage adhesive film, multiple attaching/releasing of reflection sheet to/from adherent can be possible and thus the present invention has been made as a result.